The Explanatory Power of Modal Rationalism

Abstract

Probably, the main objection to Chalmersian conceivability-based modal rationalism is that it cannot explain non-trivial essentialist de re modal knowledge. In particular, Sonia Roca-Royes has argued that the proponents of that view are not capable of elucidating our knowledge of interesting essentialist principles, such as the Essentiality of Origin and the Essentiality of Kind (let us say, by arguing that scenarios in which these principles are false are inconceivable) without presupposing essentialism in advance. I argue that this criticism is not metaphysically innocent, and that it can be handled once it is unfolded which theory of objecthood it presupposes. By using Gilbert Ryles’s distinction between strong and weak reductio ad absurdum and pluralism in geometry as illustrations (elsewhere, I have argued that such pluralism is in accordance with modal rationalism independently of whether modal monism is true or not), I draw the distinction between absolute and relative conceivability, arguing that the conceivability (or inconceivability) of scenarios that falsify the Essentiality of Kind and the Essentiality of Origin depends on which system of metaphysical axioms (or a set of beliefs) is presupposed. In the former case, conceivability is premised on a conception of objecthood one endorses, whereas in the latter case, some other metaphysical axioms are relevant as well. An advantage of the proposed reply to Roca-Royes’s criticism over David Chalmers’s own reply is that it does not depend on the validity of an anti-realist view of modality.